We have demonstrated that certain characteristic morphological features of human D- and G-group chromosomes in cells of patients with proliferative disorders may results from, in part, the presence of rearranged or additional rDNA sites. Using hybridization in situ, rDNA sites have been localized to Q-terminal positions in Dq positive and Dq negative chromosomes, and possibly certain G-group chromosomes. Cytological silver staining indicates that such sites may be transcriptively inactive. It is the focus of the proposed research (a) to determine the extent of rDNA site rearrangement and the possible relationship to chromosome morphology and specific disease state (b) to use several criteria to evaluate whether such sites are transcriptively active or inactive and how this relates to the metabolic state of the neoplastic cell and (c) to analyze possible structural changes in the DNA sequences of the repositioned rDNA complex.